1. Field of the Invention
The invention relates to flat panel display handling devices and, more particularly, to a system for transferring a flat panel display between normal atmospheric conditions and vacuum conditions.
2. Description of Related Art
The manufacturing of flat panel displays (FPDs) involves numerous complicated and specialized steps. Many of these steps must be performed in vacuum conditions. An example is the requirement of vacuum conditions for voltage contrast, or E-beam inspection methods which determine the integrity of a manufactured FPD pixel array and locate and identify defects therein. E-beam testing requires directing a beam of electrons in a vacuum at the substrate under inspection, and measuring secondary electron emission from the substrate. The voltage characteristics of the secondary electron emission signal is indicative of the electrical integrity of the substrate and can be used to locate and identify defects in the switching thin-film transistor (TFT) array of the FPD. Other applications of vacuum conditions during FPD manufacture are etching or deposition of materials.
Some of the FPD manufacturing steps are similar to those followed during, for example, semiconductor wafer manufacturing. In some situations, similar handling equipment can be used during manufacture and inspection of either the flat panel displays or the semiconductor wafers. However, new technology has enabled greater physical size of FPDs, and new constraints peculiar to FPD handling equipment have emerged. As a result, equipment which would have been adequate otherwise for use in both the FPD and the semiconductor manufacturing contexts with little modification has thus lost this versatility.
An example is vacuum handlers, which serve to transfer the workpiece between normal atmospheric conditions and vacuum conditions. FIG. 1 shows a vacuum handler of the prior art. During operation, vacuum chamber 20 is kept under high vacuum with a vacuum pumping system 24. A workpiece 12 is introduced first into a vacuum lock 14 without disruption of the vacuum integrity of the chamber 20. Then, using the same vacuum system 24 or a dedicated system (not shown), the vacuum lock 14 is evacuated until its pressure is about the same as that of vacuum chamber 20. Vacuum lock 14 is then opened into the chamber 20 and the workpiece 12 is transferred from the vacuum lock 14 onto a stage 16 or a similar work mechanism disposed within vacuum chamber 20. In this manner, a relatively high speed transfer of the workpiece 12 is effected since the volume of the vacuum lock 14 is typically much smaller than that of the vacuum chamber, requiring less time to evacuate.
U.S. Pat. No. 5,098,245 to Toro-Lira et al. and assigned to U.S. Phillips Corporation, is directed to a system for the handling of semi-conductor wafers and their transport into and out of a vacuum chamber. As is shown in FIG. 2 schematically illustrating the operation of the Toro-Lira system, a vacuum handler 15 is provided with a main vacuum chamber 22 and a vacuum lock 18. Vacuum lock 18 is sealed from the atmosphere by a circular outer door 21 shown in the closed position (21) and in an open position (21a). A circular elevator assembly 17 seals the vacuum lock 18 from the main vacuum chamber 22 using an inflatable seal 19 when the elevator assembly 17 is in the up position (solid lines). The seal 19 is shown in the inflated, or pressurized position. The sealing occurs in the cross-section opening of the main vacuum chamber 22. When the seal 19 is deflated, the elevator assembly 17 can be moved to the down position (17a) illustrated in phantom.
Operation of vacuum handler 15 is as follows: When the elevator assembly 17 is in the up position and the inflatable seal 19 pressurized, the vacuum lock 18 is vented to atmospheric conditions and outer door 21 lifted to the open position (21a). An external mechanism (not shown) transfers (arrow T.sub.1) the semiconductor wafer 23 to the top of the elevator assembly 17 in the vacuum lock 18 region. Once the wafer is inserted in vacuum lock 18, the outer door 21 is moved to the closed position and the vacuum lock 18 evacuated.
When a sufficiently low pressure is achieved in vacuum lock 18, inflatable seal 19 is deflated and the elevator assembly 17 is moved to the down position (17a), carrying with it wafer 23 into the main vacuum chamber 22. At this point, an internal mechanism (not shown) transfers (arrow T.sub.2) the wafer 23 into a vacuum chamber stage (not shown) and processing in the vacuum conditions commences. The reverse of the above procedure is subsequently followed when the processing is completed to thereby return the wafer 23 to the exterior 8 the vacuum handler 15.
The above system provides the advantage of a very fast wafer insertion process due to the relatively low volume of the vacuum lock 18 as compared with that of the main vacuum chamber 22, and dimensionally, the system is well suited for semi-conductor wafer handling. However, the advent of ever-larger flat panel displays has made applications of the conventional vacuum handlers an increasingly difficult task in FPD manufacture. Accommodation of large area FPDs by the vacuum handlers of the prior art is complicated because of the great forces developed by the high pressure differences involved, which present physical barriers taxing the limits of available materials and technology.
The limitations become evident when actual numbers are calculated and examined for the systems of the prior art. For example, in the configuration of FIG. 2, atmospheric pressure subjects the elevator assembly 17 to a very high vertical force when the outer door is in the open position (21a). For relatively small workpieces such as a 300 mm semiconductor wafer having an area of 0.0707 m.sup.2, a mechanical implementation of the elevator assembly 17 which properly counteracts the atmospheric pressure is possible. However, for larger samples such as a 1100.times.1100 mm FPD substrate, the atmospheric pressure force that needs to be compensated for is approximately 27,560 lbs., or 12 tons. A practical prior art implementation of an elevator assembly mechanism which can sustain such a high vertical force in the requisite fast and reliable manner is not possible without introducing prohibitively high costs to the system. A need therefore exists to develop a vacuum handler that can withstand the high pressures attendant to the transport of workpieces between atmospheric and vacuum conditions in a fast, reliable and economical fashion.